Dynamic range in photography represents the ratio between light intensity captured in the brightest part of the image and the darkest part of the image. Film or an image sensor is exposed to light for a set time, known as the exposure time, and the film or image sensor reacts to the amount of light that strikes the surface of the film or image sensor during that time. Typically, the recording medium (i.e., film or pixel sites in the image sensor) has a limit to the range of intensities that can be recorded. For example, if the exposure time is short, the recording medium may not capture enough light in darker parts of the image to record details about the object in the scene. In other words, part of the image is underexposed. Similarly, if the exposure time is long, the recording medium may capture too much light in brighter parts of the image such that details about the object are washed out. In other words, part of the image is overexposed.
High-dynamic range imaging uses multiple images of nearly the same scene captured using different exposure settings to create an image that has a higher dynamic range than a single image captured using a single exposure setting with the recording medium. For example, a series of three or more images may be captured using a digital camera in short succession changing the exposure time and/or aperture size for each image. These images are then blended to increase the dynamic range of the composite image, enabling details to be shown in both darker areas and lighter areas of the same image.
Because the images in the high-dynamic range (HDR) image stack are captured at different times, objects in the image may have shifted. In other words, both the camera could have shifted (e.g., if the camera is hand-held) or objects could be moving within the frame. Blending the images without adjusting for this motion causes ghosting where objects that move appear translucent and are seen in two places at once. Existing techniques can be used to find a match for each pixel in a reference image to a corresponding pixel in a second image. However, conventional techniques are either robust but slow (i.e., the techniques can't be performed at interactive frame rates and may take minutes to register a single set of HDR images) or fast but inaccurate (i.e., the blending still leaves visible image artifacts that are disturbing to a viewer). Some applications require HDR registration and blending to be performed at interactive frame rates (such as when viewing HDR video in real-time) while not sacrificing the quality of the product. Thus, there is a need for addressing these issues and/or other issues associated with the prior art.